A wide variety of vehicle braking systems may be found in the prior art. A myriad of applications ranging from small passenger vehicles to large, tractor semi-trailer trucks, employ differing structure and control methods to achieve the common goal of effectively and reliably decelerating the vehicle. The advent of inexpensive microprocessors has enabled more sophisticated control strategies. As is well known, a typical microprocessor based control system receives signals from vehicle sensors to monitor various vehicle operating parameters. This information is then used by a control program which energizes appropriate outputs to effect control of the vehicle.
Articulated vehicles, such as tractor semi-trailer trucks, often present unique problems in designing a braking system which are not encountered when designing braking systems for small passenger vehicles. One such problem is the number and location of braking sites required to properly decelerate a large articulated vehicle compared to those required for a small passenger vehicle. Typically, articulated vehicles require brakes on each segment of the vehicle. The braking control system must coordinate control of the various brake sites such that they operate in concert to properly decelerate the vehicle. Coordinated control may be accomplished with a single electronic control unit (ECU), or utilizing multiple processors arranged in a master/slave configuration.
Typically, more sophisticated control strategies require more information pertaining to the current vehicle operating parameters. This allows the control system to dynamically respond to changing operating conditions. Often, a number of operating modes are utilized to better respond to the current operating conditions. For example, a vehicle braking system may have a work balancing mode, a proportioning mode, and an anti-lock braking mode. The proper mode is selected based on the current operating conditions as determined by various vehicle sensors.
The object of a work-balanced braking mode, as its name suggests, is to balance the work performed in decelerating the vehicle among the various braking sites. The work performed at a particular braking location depends upon a number of factors. These factors may include the pressure delivered to the braking location, the number of brake sites at that location, the loading of the vehicle at that location, and the performance characteristics of the individual brakes at that location.
The braking system ECU utilizes this information to balance the work performed at the various brake locations by controlling the pressure delivered to each location. Thus, to achieve proper work balancing, it is necessary to determine how a particular location will respond to a particular delivered pressure relative to other braking locations. This relationship may be characterized by determining a relative brake factor for each braking location.
It would therefore be desirable to provide a method and system for determining relative brake factors. Once the relative brake factors are known, the vehicle braking system ECU can use this information to effect a work-balanced braking mode by delivering the appropriate amount of braking pressure to each braking location.